1. Field of the Invention
The present invention relates to a fluid pressure driving system for a vehicle.
2. Description of the Related Art
In a conventional fluid pressure driving system which is shown in Japanese Patent Laid-open Print No. Sho61(1986)-215417, a power steering device associated with a steering wheel, an oil pump, and a hydraulic motor for rotating a cooling fan are connected in series for establishing a fluid circuit, and a switching valve is provided across the hydraulic motor. In the foregoing fluid pressure driving system, if the steering wheel is rotated through an angle while the vehicle is at rest or travelling at a low speed, the switching valve is brought into an open condition, regardless of the temperature of the engine cooling water, in order to supply fluid with top priority from the oil pump to the power steering device. This is due to the fact that such steering operation requires a large amount of fluid.
However, if the large amount of fluid is supplied to the power steering device, an insufficient amount of fluid may be supplied to the hydraulic motor, which may result in a low rotational speed of the cooling fan. This may render the cooling fan ineffective and, given a high temperature of the engine cooling water, there may be a fear of overheating of the engine.